The present invention relates to switched-line type phase shifters for use at microwave and millimeter wave frequencies.
Switched-line type phase shifters can be either transmission type (two-port) or reflection type (one-port) phase shifters. A switched line type phase shifter which provides a selectable relative phase shift of either 0.degree. or .phi..degree. includes two different transmission lines and a switch system for selecting either one as the transmission path to be followed by the signal to be phase shifted. The transmission line which constitutes the signal path when a relative phase shift of .phi..degree. is selected is made electrically longer than the transmission line which constitutes the signal path when a relative phase shift of 0.degree. is selected. This difference in electrical length is selected to provide a difference in transmission time of .tau..sub.o seconds where ##EQU1## where T.sub.o is the period of a signal at the design operating frequency F.sub.o at which a phase shift of .phi..degree. is desired. As a function of frequency the relative phase shift .phi. provided by such a phase shifter is .phi.=(360.degree.).tau..sub.o F, where F is the operating frequency. Thus, the phase shift .phi. is a function of frequency.
This frequency dependency of the phase shift provided by a switched-line type phase shifter restricts its use to narrowband systems when tight tolerances are placed on the phase shift provided.
Various systems such as radar and communication systems are desired which operate in the microwave (3 GHz to 30 GHz) and millimeter-wave frequency ranges (30 GHz to 300 GHZ). A number of different components needed for the construction of such microwave and millimeter wave systems are being developed. Many such systems require compact and controllable phase shifters having low loss and low phase variation over a substantial operating frequency band. Switched-line type phase shifters are applicable to this frequency range, however, their use has not been feasible in wideband systems.
It is desirable to provide a compact, electrically controllable, switched-line type phase shifter operating in the microwave and millimeter wave frequency ranges and having low loss and low phase variation over a wide operating frequency band.